High-fidelity two-qubit gate and teleportation with mobile spins

Efficient quantum error correction in spin qubit systems relies on strong qubit connectivity within the architecture [1]. In semiconductor heterostructures, exchange-based two-qubit interactions are typically limited to nearest-neighbor couplings due to their intrinsic short range. To overcome this limitation, recent advancements have focused on utilizing superconducting resonators [2] and on physically displacing spin qubits. A particularly appealing method for moving spins around is conveyor-style shuttling [3-5], which employs phase-shifted sinusoidal gate voltages to transport single charges in moving quantum dots.

This work presents a high-fidelity controlled-Z (CZ) gate, activated by bringing two electron spins close together by conveyor-shuttling. The spins are confined in a channel defined in a ²⁸Si/SiGe heterostructure that can host a linear array of six quantum dots. By shuttling each electron to the array's midpoint, a saturation of the exchange coupling can be observed. The CZ fidelity, assessed through randomized benchmarking, reaches 99.4%. We next utilize the conveyor-style two-qubit gate to accomplish quantum state teleportation. Specifically, the quantum state of the spin localized in dot 6 is conditionally teleported to the spin located in dot 2.



[1] Xu et al., Nature Physics 20, 1084–1090 (2024)

[2] Dijkema et al., Nature Physics (2024)

[3] Struck et al., Nature Communications 15, 1325 (2024)

[4] Xue et al., Nature Communications 15, 2296 (2024)

[5] De Smet, Matsumoto et al., arXiv.2406.07267 (2024)